In a conventional electrophotographic image forming device, an electrostatic latent image is formed on a photosensitive drum. Toner accommodated within a developing cartridge is supplied to the electrostatic latent image, thereby forming a toner image on the photosensitive drum. The toner image is then transferred onto a sheet to form an image on the sheet.
One of such conventional developing cartridges includes a casing, a toner accommodation chamber for storing toner therein, a developing roller rotatably supported to the casing, a leaf spring whose one end is supported to the casing, a thickness regulation member disposed in opposition to the developing roller, and sealing members disposed on both widthwise ends of the developing roller. The thickness regulation member includes a thickness regulating section formed of an insulative silicon rubber and attached to another end of the leaf spring. The sealing member is in contact with an outer circumferential surface of the developing roller and is attached to the leaf spring for sealing a gap between the developing roller and the thickness regulating section to prevent toner from leaking outside from the casing.